BETA-CYCLODEXTRIN EFFECTS ON THE PHOTO-FRIES REARRANGEMENT OF AROMATIC ALKYL ESTERS

The photolysis of phenyl propionate (1a) and phenyl valerate (1b) in water and in solutions containing beta-cyclodextrin (CD) leads to the corresponding p-hydroxyphenyl alkyl ketone 2, o-hydroxyphenyl alkyl ketone 3, and phenol 4. When the reactions are carried out in the presence of oxygen there is a decrease in the total amount of rearrangement products, but the inhibition is less marked in the presence of CD. The [3]/[2] ratio for 1b increases when CD concentration changes from 0 to 10 mM. These changes are due to the increase in the quantum yield for the formation of 3 and a decrease in the quantum yield for 2 in solutions containing CD. The [3]/[2] ratio for la decreases in the presence of CD although both quantum yields increase with CD concentration. Under the conditions used in this study, the substrate reacted in the bulk solution and in the cavity of CD. The quantum yields for the formation of 3 and 4, PHI(CD)3 and PHI(CD)4, are higher for the included substrate than the corresponding values for the free substrate while PHI(CD)2 is higher than PHI(w)2 for 1a but lower for 1b. This effect is attributed to the different orientation of the substrates in the cavity of CD. Besides, PHI(CD)4 also increases due to the availability of hydrogens bonded to secondary carbons in the cavity of the cyclodextrin.